Method for manufacturing wiring circuit boards with bumps and method for forming bumps

ABSTRACT

Wiring circuit boards with bumps can be manufactured such that stable bump connections are possible and plating pre-treatments or other difficult operations are rendered unnecessary. By utilizing a technique whereby a bump-formation etching mask  7  is formed on a bump-forming surface  3   a  of a metal foil  3  which has a thickness that is the sum of the thickness t 1  of the wiring circuit  1  and the height t 2  of the bumps  2  which are to be formed on the wiring circuit  1  (t 1+ t 2 ), and then the bumps  2  are formed by half-etching the metal foil  3  to a depth corresponding to the desired bump height t 2  from the bump-formation etching mask  7  side, wiring circuit boards with bumps can be manufactured such that stable bump connections are possible and plating pre-treatments or other complex processes are rendered unnecessary.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method-for manufacturing awiring circuit board which has bumps of a constant fixed height.

[0003] 2. Description of the Related Art

[0004] Very small bumps (e.g., 50 μm in diameter and 30 μm in height)are widely used in connections between electronic component elementssuch as semiconductor or LCD elements and wiring circuit boards, orbetween the different layers in multilayered wiring substrates.

[0005] A representative method for manufacturing bumps of such size isgiven in FIGS. 4A to 4E.

[0006] In other words, first, a dual-layer flexible substrate 43comprising a copper foil 42 affixed to a polyimide film 41 is prepared,as shown in FIG. 4A, after which the copper foil 42 is patterned using aphotolithography technique to form a wiring circuit 44 (FIG. 4B).

[0007] Next, a cover coat layer 45 is formed on the wiring circuit 44 inaccordance with a conventional method (FIG. 4C). For example, it ispossible to form the cover coat layer 45 by forming a polyamic acidlayer on the wiring circuit 44, patterning it using photolithography andimidising it. A resist ink can also be printed thereon.

[0008] Next, very small bumps can be formed by irradiating with a laserlight the region of the polyimide film 41 which corresponds to thewiring circuit 44 to form bump holes 46 (FIG. 4D), and then, using anelectrolytic plating method to form metal bumps 47 on the wiring circuit44, which is exposed in the bottom portion of the bump holes 46. Thecover coat layer 45 may be optionally covered with a protective film(not shown) after the irradiation and before the electrolytic plating(FIG. 4E).

[0009] However, when the bump holes 46 are formed by the irradiationwith the laser light, the surface area of the openings will vary, owingto scattering in the amount of smearing attached to the bottom portionof the bump holes 46; therefore a drawback arises in that substantialscattering appears in the height of the metal bumps 47. Accordingly,stable bump connections become difficult to achieve. Connectingsemiconductor elements to the wiring circuit in one step usingultrasonic waves becomes particularly difficult. Plating pre-treatmentsbecome essential, moreover, in order to improve the adhesive strengthbetween the wiring circuit 44 and the metal bumps 47 formed thereon.

SUMMARY OF THE INVENTION

[0010] In view of the foregoing problems of prior art, it is an objectof the present invention to provide a method for manufacturing a wiringcircuit board with bumps, which enables stable bump connections andfurthermore does not require complex operations such as platingpre-treatments.

[0011] The inventors have perfected the present invention based on thediscovery that stable bump connections can be effected by half-etching ametal foil, which is of a thickness that is the sum of the thicknesscorresponding to the height of the metal bumps and the thickness of thewiring circuit layer, to a depth corresponding to the thickness of themetal bumps, it is possible to fabricate bumps of uniform height,without requiring complex operations such as plating pre-treatments.

[0012] The present invention provides a method for the manufacture of awiring circuit board having a wiring circuit and bumps formed thereon,comprising the steps of (a) laminating a protective film onto onesurface of a metal foil on which bumps are to be formed, which is of athickness that is the sum of the thickness of the wiring circuit and theheight of bumps which are to be formed on the wiring circuit and forminga wiring circuit formation etching mask on the other surface of themetal foil where the wiring circuit is to be formed; (b) forming thewiring circuit to a desired thickness by half-etching the metal foilfrom the wiring circuit-formation etching mask side; (c) providing acover coat layer on the wiring circuit, after removing the wiringcircuit-formation etching mask; (d) forming a bump-formation etchingmask on the bump formation surface, after removing the protective filmwhich has been provided on the bump formation surface of the metal foil;(e) forming bumps to a desired height by half-etching the metal foilfrom the bump-formation etching mask side; (f) forming a polyimideprecursor layer so as to bury the bumps, after removing thebump-formation etching mask; and (g) forming an insulating later of adesired thickness by etching back and then imidising the polyimideprecursor layer. The wiring circuit can be formed before the bumps areformed, by using this method of manufacture.

[0013] Moreover, the present invention provides a method for themanufacture of a wiring circuit board having a wiring circuit and bumpsformed thereon, comprising the steps of: (aa) laminating a protectivefilm onto one surface of a metal foil on which a wiring circuit is to beformed, which is of a thickness that is the sum of the thickness of thewiring circuit and the height of bumps which are to be formed on thewiring circuit and forming a bump-formation etching mask on the othersurface of the metal foil where the bumps are to be formed; (bb) formingthe bumps to a desired height by half-etching the metal foil from thebump-formation etching mask side; (cc) forming a polyimide precursorlayer so as to bury the bumps, after the bump-formation etching mask hasbeen removed; (dd) forming an insulating layer of a desired thickness byetching and then imidising the polyimide precursor layer; (ee) forming awiring circuit formation etching mask on the wiring circuit formationsurface, after removing the protective film which has been provided onthe wiring circuit formation surface of the metal foil; (ff) forming awiring circuit to a desired thickness by half-etching the metal foilfrom the wiring circuit-formation etching mask side; and (gg) providinga cover coat layer on the wiring circuit, after removing the wiringcircuit formation etching mask. Bumps can be formed before the wiringcircuits are formed, by using this method of manufacture.

[0014] Moreover, the present invention provides a method for formingbumps, comprising forming a bump-formation etching mask on the bumpformation surface of a metal foil of a thickness that is the sum of thethickness of the wiring circuit and the height of the bumps which are tobe formed on the wiring circuit, and half-etching the metal foil to adepth corresponding to a desired bump height from the bump-formationetching mask side.

[0015] Furthermore, the present invention provides a wiring circuitboard, comprising a wiring circuit, a cover coat layer formed on onesurface of the wiring circuit, an insulating layer formed on the othersurface of the wiring circuit, and bumps which are connected to thewiring circuit and formed so as to protrude from the insulating layer,wherein the wiring circuit and the bumps are formed from one metal foil.It is preferable to form a contact hole in the cover coat layer toenable electric connection to the wiring circuit from the cover coatlayer side. The insulating layer is preferable to be a polyimide layerobtained by imidising a polyimide precursor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIGS. 1A to 1G are process diagrams illustrating a method ofmanufacturing wiring circuit boards with bumps pertaining to the presentinvention;

[0017]FIGS. 2A to 2G are process diagrams illustrating a method ofmanufacturing wiring circuit boards with bumps pertaining to the presentinvention;

[0018]FIGS. 3A and 3B are process diagrams illustrating a method forforming bumps; and

[0019]FIGS. 4A to 4E are process diagrams illustrating a conventionalmethod of manufacturing wiring circuit boards with bumps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be described stepwise in furtherdetail with reference to the drawings.

[0021] First, a method of manufacturing wiring circuit boards with bumpswherein bumps are formed on the wiring circuit shall be describedstepwise with reference to FIG. 1, as a method of manufacture whereinwiring circuits are formed prior to bumps (Steps (a) through (g)).

[0022] Step (a)

[0023] First, a protective film 4 is laminated onto a bump-formingsurface 3 a of a metal foil 3, which is of a thickness that is the sumof the thickness t1 of a wiring circuit 1 (shown as a dotted line in thedrawing) and the height t2 of bumps 2 (shown as a dotted line in thedrawing) which are to be formed on the wiring circuit 1, and a wiringcircuit-formation etching mask 5 is formed on a wiring circuit-formationsurface 3 b of the metal foil 3 (FIG. 1A).

[0024] A value which is maximally suited to the objective of applicationfor the wiring circuit board is to be selected for the wiring circuitthickness t1 and the bump height t2. For example, the thickness t1 ofthe wiring circuit 1 can be set to 20 μm, the height t2 of the bumps 2to 30 μm and the diameter of the bumps 2 to 50 μm when using wiringcircuit boards as semiconductor element mounting substrates.

[0025] A material which is used in wiring circuit board conductor layerscan be employed for the metal foil 3, with copper foil being preferred.

[0026] The wiring circuit-formation etching mask 5 can be formed byscreen-printing a resist ink onto the wiring circuit formation surface 3b of the metal foil 3. Alternatively, the mask can be formed byproviding a photosensitive resin layer or dry film thereon, thenpatterning it through exposure and development according to aconventional method.

[0027] Step (b)

[0028] Next, the wiring circuit 1 of desired thickness t1 is formed byhalf-etching the metal foil 3 from the wiring circuit formation etchingmask 5 side (FIG. 1B).

[0029] The half-etching conditions (temperature, etchant solutioncomposition etc.) are to be suitably selected in accordance withmaterial used for the metal foil 3, the thickness which should beremoved by etching, etc.

[0030] Step (c)

[0031] Next, a cover coat layer 6 is provided on the wiring circuit 1,after the wiring circuit formation etching mask 5 has been removed usinga conventional method (FIG. 1C) The cover coat layer 6 can be formed byscreen-printing a cover coat layer coating thereon. Alternatively, aphotosensitive resin layer or dry film can be provided thereon and thenpatterned by exposure and development according to a conventionalmethod. Moreover, a layer comprising polyamic acid or another polyimideprecursor can be provided thereon, then patterned and imidised.

[0032] Step (d)

[0033] A bump-formation etching mask 7 is formed on the bump-formingsurface 3 a after the protective film 4, which has been provided on thebump-forming surface 3 a of the metal foil 3, has been removed accordingto a conventional method (FIG. 1D).

[0034] The bump-formation etching mask 7 can be formed byscreen-printing a resist ink on the bump-forming surface 3 a of themetal foil 3. Alternatively, a photosensitive resin layer or dry filmcan be provided thereon and then patterned by exposure and developmentaccording to a conventional method.

[0035] Step (e)

[0036] Bumps 2 of desired height t2 are formed by half-etching the metalfoil 3 from the bump-formation etching mask 7 side (FIG. 1E).

[0037] The half-etching conditions (temperature, etching solutioncomposition etc.) are to be suitably selected in accordance with thematerial used for the metal foil 3, the thickness which should beremoved by etching, etc.

[0038] The cover coat layer 6 may be covered by a protective film priorto the half-etching (not shown).

[0039] Step (f)

[0040] A polyimide precursor layer 8 is formed so as to bury the bumps2, after the bump-formation etching mask 7 has been removed according toa conventional method (FIG. 1F).

[0041] When the bump-formation etching mask 7 is to be removed, theprotective film may be removed at the same time, should the cover coatlayer 6 be covered by the film.

[0042] Moreover, the polyimide precursor layer 8 can be provided byforming a film from polyamic acid etc. according to a conventionalmethod. The conditions for imidisation can be determined according tothe type of polyimide precursor employed.

[0043] Step (g)

[0044] The polyimide precursor layer 8 is etched back and imidised toform a insulating layer 9 of the desired thickness t3. The wiringcircuit board with bumps of the present invention as shown in FIG. 1Gcan be thereby obtained. This wiring circuit board comprises the wiringcircuit 1, the cover coat layer 6 formed on one surface of the wiringcircuit 1, the insulating layer 9 formed on the other surface of thewiring circuit 1, and bumps 2 which are connected to the wiring circuit1 and formed so as to protrude from the insulating layer 9. Asignificant feature of the wiring circuit board of the present inventionresides in that the wiring circuit and the bumps are formed from onemetal foil. It is preferred that contact holes 10 are formed in thecover coat layer 6 to enable electric connection to the wiring circuit 1from the cover coat layer side. The insulating layer 9 is preferable tobe a polyimide layer obtained by imidising a polyimide precursor.

[0045] Next, a method of manufacturing wiring circuit boards with bumpswherein bumps are formed on the wiring circuit shall be describedstepwise with reference to FIG. 2, as a method of manufacture whereinthe bumps are formed prior to the wiring circuits (Steps (aa) through(gg)). The structural elements indicated by the symbols in FIGS. 2A to2G correspond to the structural elements of the same symbols in FIGS. 1Ato 1G.

[0046] Step (aa)

[0047] First, a protective film 4 is laminated onto a wiring circuitformation surface 3 b of a metal foil 3, which is of a thickness that isthe sum of the thickness t1 of the wiring circuit 1 (shown as a dottedline in the drawing) and the height t2 of bumps 2 (shown as a dottedline in the drawing) which are to be formed on the wiring circuit 1, anda bump-formation etching mask 7 is formed on a bump-forming surface 3 aof the metal foil 3 (FIG. 2A)

[0048] Step (bb)

[0049] The bumps 2 of desired height t2 are formed by half-etching themetal foil 3 from the bump-formation etching mask 7 side (FIG. 2B).

[0050] Step (cc)

[0051] A polyimide precursor layer 8 is formed so as to bury the bumps2, after the bump-formation etching mask 7 has been removed according toa conventional method (FIG. 2C).

[0052] Step (dd)

[0053] The polyimide precursor layer 8 is etched back and imidised toform a insulating layer 9 of the desired thickness t3 (FIG. 2D).

[0054] Step (ee)

[0055] The wiring circuit formation etching mask 5 is formed on thewiring circuit formation surface 3 b, after the protective film 4 whichhas been provided on the wiring circuit formation surface 3 b of themetal foil 3 has been removed according to a conventional method (FIG.2E).

[0056] Step (ff)

[0057] Wiring circuits 1 of desired thickness t1 are formed byhalf-etching the metal foil 3 from the wiring circuit formation etchingmask 5 side (FIG. 2F).

[0058] The bumps 2 may be covered by a protective film prior to thehalf-etching (not shown).

[0059] Step (gg)

[0060] The cover coat layer 6 is provided the wiring circuit 1, afterthe wiring circuit formation etching mask 5 has been removed accordingto a conventional method. The wiring circuit board with bumps shown inFIG. 2G, which has the same structure as that of wiring circuit board asshown in FIG. 1G, can be thereby obtained.

[0061] When the wiring circuit formation etching mask 5 is to beremoved, the protective film may be removed at the same time, should thebumps 2 be covered by the film.

[0062] If the methods of manufacturing wiring circuit boards with bumpsas described in FIGS. 1A to 1G and FIGS. 2A to 2G are viewed from theperspective of being methods for forming bumps, then the method forforming bumps as depicted by FIGS. 3A and 3B can be educed.

[0063] In other words, a bump-formation etching mask 7 is formed on thebump-forming surface 3 a of the metal foil 3 which has a thickness thatis the sum of the thickness t1 of the wiring circuit 1 and the height t2of the bumps 2 which are to be formed on the wiring circuit 1 (t1+t2)(FIG. 3A), and then, as shown in FIG. 3B, the bumps 2 can be formed byhalf-etching the metal foil 3 to a depth corresponding to the desiredbump height t2 from the bump-formation etching mask 7 side. In such acase, it is allowable for the wiring circuit 1 to be worked after theforming of bumps 2, and it is also allowable for the bumps 2 to beformed after the wiring circuit 1 has been worked.

[0064] The height of the bumps thereby obtained is kept uniform and thecombined thickness of the wiring circuit and the bumps is also keptconstant. Stable bump connections are thereby made possible.

[0065] According to the present invention, wiring circuit boards withbumps can be provided wherein the bump strength is stable, stable bumpconnections are possible and plating pre-treatments or other complexprocesses are rendered unnecessary. The bump connections in integratedcircuits in particular can be made stably, in one step, using ultrasonicwaves.

[0066] The entire disclosure of the specification, claims and drawingsof Japanese Patent Application No. 11-319669 filed on Nov. 10, 1999 ishereby incorporated by reference.

What is claimed is:
 1. A wiring circuit board, comprising a wiring circuit, a cover coat layer formed on one surface of the wiring circuit, an insulating layer formed on the other surface of the wiring circuit, and bumps which are connected to the wiring circuit and formed so as to protrude from the insulating layer, wherein the wiring circuit and the bumps are formed from one metal foil.
 2. The wiring circuit board according to claim 1, wherein a contact hole is formed in the cover coat layer to enable electric connection to the wiring circuit from the cover cost layer side.
 3. The wiring circuit board according to claim 1, wherein the insulating layer is a polyimide layer obtained by imidising a polyimide precursor. 